The present invention relates to microfabricated actuators, particularly to microactuators for use in catheter-based interventional therapies or remote micro-assembly applications, and more particularly to microfabricated therapeutic actuators utilizing shape memory polymer microtubing as a release actuator mechanism.
Microactuators for remote and precise manipulation of small objects is of great interest in a wide variety of applications. Recently, substantial efforts have been directed to the development of microactuators or microgrippers for various application, and which are particularly useful in the medical field, such as for catheterbased intervention therapies and remote assembly or use of micromechanical systems. There has been particular interest in the development of microactuators capable of operating in small (250-500 .mu.m) diameter applications, such as in veins in the human brain, which enables catheter-based devices to reach and treat an aneurysm in the brain.
A recent approach to satisfying this need involves microactuators or microgrippers fabricated using known silicon-based techniques or precision micromachining, or a combination of these techniques, with the microgrippers being actuated, for example, by balloons or by shape-memory alloy (SMA) films or wires deposited on or connected to the jaws of the microgrippers. Such an approach is described and claimed in copending U.S. application Ser. No. 08/446,146, filed May 22, 1995, entitled "Microfabricated Therapeutic Actuator Mechanism", now U.S. Pat. No. 5,645,564 issued Jul. 8, 1997, assigned to the same assignee. Another recent approach involves a miniature plastic gripper constructed of either heat-shrinkable or heat-expandable plastic tubing having a cut in one end section to form gripping surfaces or jaws which are moved by inflation or deflation of an associated microballoon. Such an approach is described and claimed copending U.S. application Ser. No. 08/549,497, filed Oct. 27, 1995, entitled "Miniature Plastic Gripper And Fabrication Method", now U.S. Pat. No. 5,609,608 issued Mar. 11, 1997, assigned to the same assignee. Also, microdevices for positioning, steering, and/or sensor applications have been developed which utilize blood flow for positioning and steering of catheter-based therapeutic applications. Such microrudders, microactuators or microcantilevers are described and claimed in copending U.S. application Ser. No. 08/533,426, filed Sep. 25, 1995, entitled "Micromachined Actuators/Sensors For Intratubular Positioning/Steering", assigned to the same assignee. In addition, recent efforts have been directed to the fabrication of micromolds for the production of microballoons used, for example, angioplasty to perform interventional catheter-based minimal-invasive surgeries, wherein microballoons or microneedles having, for example, a 275 .mu.m length and 150 .mu.m diameter can be readily manufactured. Such a micromold is described and claimed in copending U.S. application Ser. No. 08/533,425, filed Sep. 25, 1995, entitled "Polymer Micromold And Fabrication Process", now U.S. Pat. No. 5,658,515 issued Aug. 19, 1997.
Patients with potentially life-threatening hemmorhagic brain aneurysms are in need of a safe, reliable, and fast release mechanism for the deposition of embolic platinum coils via catheters. The commercial product of current use is the Guglielmi Detachable Coil (GDC). The GDC utilizes the electrolytical dissolution of a designated guidewire junction to generate the release action. This procedure typically takes 10-30 minutes and is difficult to control in a reliable fashion. The effects of the dissolved material into the blood stream is also a potential hazard to the patient. Thus, even with the numerous prior efforts to development miniature actuators for catheter-based therapeutic application, there remains a need for safe, fast release actuator mechanisms for the delivery of embolic coils, for example.
The present invention satisfies this need, and is based on shape memory polymer (SMP), and polyurethane-based material that undergoes a phase transformation at a manufactured temperature (Tg) of choice. After the material is polymerized (cross-linked), the material is molded into its memory shape. At temperatures above Tg, the material can be easily reshaped into another configuration, and upon cooling below Tg the new shape is fixed, but upon increasing the temperature to above Tg, the material will return to its original memory shape. By inserting a GDC, for example, into an end of a SMP microtube, and applying pressures to the outside of the microtube while at a temperature above the Tg and then lowering the temperature below the Tg, the GDC is secured and retained in the microtube. After inserting the microtube and retained GDC via a catheter to a desired location, the SMP microtube is locally heated to above Tg and it returns to its original shape releasing the GDC, after which the microtube is withdrawn leaving the GDC in place.